Kochhann, Karlos G.D., Holbourn, Ann, Kuhnt, Wolfgang and Xu, Jian (2017) Eastern equatorial Pacific benthic foraminiferal distribution and deep water temperature changes during the early to middle Miocene. Marine Micropaleontology, 133 . pp. 28-39. DOI 10.1016/j.marmicro.2017.05.002.

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Abstract

We investigate changes in benthic foraminiferal assemblages and estimate bottom water temperatures (BWT), based on Mg/Ca ratios of Oridorsalis umbonatus, over three selected intervals of major climate change during the late early to middle Miocene at Integrated Ocean Drilling Program (IODP) Sites U1337 (4463 m water depth) and U1338 (4200 m water depth), eastern equatorial Pacific Ocean. The targeted intervals are: (1) the onset of the Miocene Climatic Optimum (MCO; at ~ 16.9 Ma) and associated carbon cycle perturbation (Site U1337); (2) the episode of peak warmth within the MCO centered at 15.6 Ma (Site U1338); (3) the major cooling step at ~ 13.8 Ma related to east Antarctic ice-sheet expansion (Site U1338). Assemblages from these three intervals are mainly composed of cosmopolitan, long ranging (e.g., Paleogene to recent), lower bathyal to abyssal species, including calcareous elongated forms that became extinct during the middle Pleistocene. The onset of the MCO and interval of peak warmth had little impact on benthic foraminiferal accumulation rates (BFAR), abundances and assemblage composition. A transient BWT warming of 2.6 °C at the onset of the interval of peak warmth concurred with a benthic stable oxygen isotope (δ18O) decrease of 1‰, suggesting that the δ18O decrease was largely controlled by BWT changes. A substantial increase in BFAR and in the abundances of Epistominella exigua and epifaunal taxa after ~ 13.83 Ma coincides with increased opal accumulation rates, reflecting enhanced and seasonally pulsed organic carbon (Corg) flux to the seafloor during the global cooling step. During this interval, BWT decrease by 1.7 °C concurrent with a 1.0‰ increase in the stable oxygen isotope composition of seawater (δ18Osw). Comparable trends at Ocean Drilling Program (ODP) Site 1146 in the South China Sea, with a 2.2 °C cooling and 0.9‰ increase in δ18Osw at ~ 13.8 Ma, further support that the benthic δ18O increase during the major cooling step was largely controlled by ice volume changes.

Document Type:	Article
Keywords:	Benthic foraminifera, Mg/Ca-based paleotemperatures, Miocene Climatic Optimum, Eastern equatorial Pacific Ocean, Integrated Ocean Drilling Program Sites U1337 and U1338
Research affiliation:	Kiel University > Kiel Marine Science OceanRep > The Future Ocean - Cluster of Excellence Kiel University
Refereed:	Yes
Open Access Journal?:	No
Publisher:	Elsevier
Projects:	Future Ocean
Date Deposited:	18 Jan 2018 12:18
Last Modified:	06 Feb 2020 09:07
URI:	https://oceanrep.geomar.de/id/eprint/41636

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